The present invention relates to a video signal processing apparatus that may be applied to business-use video editing equipment.
Business-use video editing equipment (digital multi-effector) includes a special effect processing feature that allows luminance and chroma information in a video signal to be controlled as desired in accordance with the objective in video editing.
FIG. 10 is a schematic flow diagram of a conventional video signal processing apparatus with the special effect processing feature. In FIG. 10, a terminal 12 receives a digitized luminance signal Y that is fed to a luminance signal special effect processing circuit (Y-dedicated effect processing circuit) 14 for special effect processing. A special effect signal generator, not shown, generates a special effect signal for use with the luminance signal. This special effect signal (such as a posterization signal) is supplied to the processing circuit 14.
A terminal 16 receives a digitized chroma signal C that is converted by a color difference signal generation circuit 18 into color difference signals (R-Y) and (B-Y). The color difference signals are then fed to a chroma signal special effect processing circuit (C-dedicated effect processing circuit) 20 for special effect processing. The above-mentioned special effect signal generator generates another special effect signal for use with the chroma signal. The luminance signal Y and chroma signal C having undergone the special effect processing are combined by a composition circuit 22 into a composite video signal.
Where the special effect processing is carried out, the level of the composite video signal must meet relevant broadcast requirements. For example, suppose that the luminance signal Y and chroma signal C are subjected to the special effect processing and that the levels of the two signals fall within their respective predetermined ranges, as shown in FIG. 11A. In that case, combining the two signals after the processing can cause part of the processed chroma signal C' to exceed the upper limit of the broadcast requirements. Conversely, the processed chroma signal C' can drop below its lower limit depending on the special effect processing performed on the luminance signal Y.
A chroma signal C' having exceeded its upper limit level will have a distorted phase. This can lead to the generation of what is known as illegal colors. The phenomenon is conventionally suppressed by a limiter 28 installed as depicted in FIG. 10.
The luminance signal Y' and chroma signal C' having undergone the special effect processing are led into an adder 24 for signal composition. The composite video signal from the adder 24 is supplied to a control unit 26. The control unit 26 checks to see if the level of the composite video signal falls within a permissible range of relevant broadcast requirements. If the composite video signal is found to exceed its upper or lower limit, the control unit 28 effects an output to control the limiter 28 so as to limit the level of either the luminance signal Y' or the chroma signal C'. Illustratively, the gain of the chroma signal C' may be controlled for the composite video signal to meet the broadcast requirements shown in FIG. 11C.
As outlined, the conventional measures for illegal color prevention involve actually producing the composite video signal from the luminance signal Y' and chroma signal C' and then operating the control unit 28 in accordance with the produced composite signal. This translates into a bulky scale of hardware for the control unit 26.